Interleukin 4(IL4) was first identified as a helper T cell product with the capacity to co-stimulate B cell growth in vitro. IL-4 also can rescue B-cells from apoptosis, enhancing their survival, and is responsible for immunoglobulin isotype switching to IgG1 and IgE. The effect of IL-4 signaling is mediated through the IL-4 receptor alpha chain (IL-4Rα). Upon binding to its ligand, IL-4Rα dimerizes either with the common gamma chain (γc) to produce the type-1 signaling complex located mainly on hematopoietic cells, or with the IL-13 receptor alpha 1 (IL-13Rα1) to produce the type-2 complex, which is expressed also on non-hematopoietic cells. The type-1 signaling complex is critical for Th2-skewing of T cells and the development of alternatively activated macrophages (AAMΦs), while the type-2 complex plays a role in non-hematopoietic responses to IL-4 and IL-13.